1. Field of the Invention
The present invention relates to a fuel cell system that determines the offset correction value for a current detector in a fuel cell, as well as to an offset correction value determination method for a current detector used in a fuel cell system.
2. Description of the Related Art
In general, current sensors have offset current that appears when the input signal is ‘0’, and this offset current fluctuates (drifts) due to secular change. Furthermore, fuel cell current sensors are incorporated in fuel cells that become hot in operation, and because current sensors are used at high temperatures, temperature-induced temperature drift also occurs. The fuel cell power input/output balance accuracy of the fuel cell system as a whole varies widely depending on the performance of the fuel cell's current sensor. For example, while a fuel cell is generating 350 A (amperes) of power, an input/output difference of approximately 1 kW of power exists if there is a sensor error of 3 A, or approximately 1%. Therefore, improvement of the accuracy of the input/output balance of the fuel system as a whole is a critical issue.
As a technology to accurately calculate the power generation target for a fuel cell, a technology has been proposed in which multiple current sensors and voltage sensors are used in order to enable power consumption errors in each device or power consumption errors caused by line resistance to be ignored.
However, in the technology described above, the accuracy of and characteristic fluctuations in the current sensors are not taken into account, and measurement error due to zero-point fluctuation (zero drift) in the current sensors has not yet been eliminated. As a result, discrepancies occur between power generation target values and actual values, thereby preventing improvement of input/output balance accuracy for the fuel cell system as a whole.